1 METHOD AND APPARATUS FOR PROVIDING LEAK DETECTION IN DATA MONITORING AND MANAGEMENT SYSTEMS
The present invention relates to data monitoring and management systems. More specifically, the present invention relates to method and apparatus for providing leak detection in sensors used in data monitoring systems such as glucose monitoring systems.
Glucose monitoring systems including continuous and discrete monitoring systems generally include a small, lightweight battery powered and microprocessor controlled system Which is configured to detect signals proportional to the corresponding measured glucose levels using an electrometer, and radio frequency (RF) signals to transmit the collected data. One aspect of such glucose monitoring systems include a sensor configuration which is, for example, mounted on the skin of a subject whose glucose level is to be monitored. The sensor cell may use a three-electrode (work, reference and counter electrodes) configuration driven by a controlled potential (potentiostat) analog circuit connected through a contact system.
The current level detected by the work electrode of the sensor is relatively small such that even a small amount of leakage current from the reference or counter electrodes typically will affect the signal quality, and thus may have adverse effect upon the accuracy of the measured glucose level. This is especially true when foreign matter is present that causes a false high glucose reading, and which may lead to improper patient treatment. Furthermore, when the glucose monitoring system is calibrated, the offset and gain of the sensor-transmitter pair is established. If the leakage current level changes (i.e., either increases or decreases), then the offset established will likely change and a resulting gain error may result for future calibration points.
In view of the foregoing, it would be desirable to have an approach to detect leakage current in sensor configuration of data monitoring systems such as in glucose monitoring systems such that detective sensors resulting from leakage current may be identified that are not detecting signals accurately.
In view of the foregoing, in accordance with the various embodiments of the present invention, there is provided a method and apparatus for performing leak detection in the sensor of a glucose monitoring system such as continuous or discrete glucose monitoring system. The sensor may include subcutaneous or transcutaneous sensor and configured to detect glucose levels of a patient, in particular, diabetic patients.
In one embodiment, there is provided a capacitance to a guard electrode of the sensor, and a test signal is applied to the guard electrode to determine whether a current flow can be detected over the capacitance. If the test signal results in the current flow, it is determined that the current flow is as a result of the existence of leakage current in the sensor, and the user orpatient is alerted that the sensor is not functioning properly. In other words, a detection of the leakage current prompts the patient that the sensor is no longer measuring accurate glucose levels, and that replacement of the sensor is recommended.
2 BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a block diagram of a data monitoring and management system for practicing one embodiment of the present invention;
FIG. 2 is a block diagram of the transmitter of the data monitoring and management system shown in FIG. 1 in accordance with one embodiment of the present invention;
FIG. 3 illustrates the front end section of the analog interface of the transmitter in accordance with one embodiment of the present invention;
FIGS. 4A-4B respectively show detailed illustrations of the current to voltage circuit and the counter-reference servo circuit of the analog interface shown in FIG. 3 in accordance with one embodiment of the present invention;
FIG. 5 illustrates the leak detection circuit in accordance with one embodiment of the present invention;
FIGS. 6A-6B illustrate the output response of the current to voltage circuit in the transmitter of the data monitoring and management system of FIG. 1 for 100 MOhm leakage resistance between the Work and guard electrodes of the sensor with leak detection test signal held for 500 and 250 mseconds, respectively, in accordance with one embodiment of the present invention;
FIGS. 7A-7B illustrate the output response of the current to voltage circuit in the transmitter of the data monitoring and management system of FIG. 1 for 1,000 MOhm and 10,000 MOhm leakage resistance, respectively, between work and guard electrodes of the sensor, with leak detection test signal held low for 500 mseconds in accordance with one embodiment; and
FIG. 8 is a flowchart for performing the leak detection test in the sensor of the data monitoring and management system in accordance with one embodiment of the present invention.
FIG. 1 illustrates a data monitoring and management system such as, for example, a glucose monitoring system 100 in accordance with one embodiment of the present invention. In such embodiment, the glucose monitoring system 100 includes a sensor 101, a transmitter 102 coupled to the sensor 101, and a receiver 104 which is configured to communicate with the transmitter 102 via a communication link 103. The receiver 104 may be further configured to transmit data to a data processing terminal 105 for evaluating the data received by the receiver 104. Only one sensor 101, transmitter 102, communication link 103, receiver 104, and data processing terminal 105 are shown in the embodiment of the glucose monitoring system 100 illustrated in FIG. 1. However, it will be appreciated by one of ordinary skill in the art that the glucose monitoring system 100 may include one or more sensor 101, transmitter 102, communication link 103, receiver 104, and data processing terminal 105, where each receiver 1 04 is uniquely synchronized with a respective transmitter 102. Moreover, within the scope of the present invention, the glucose monitoring system 100 may be a continuous monitoring system, or a semi-continuous or discrete monitoring system.
In one embodiment of the present invention, the sensor 101 is physically positioned on the body of a user whose glucose level is being monitored. The sensor 101 may be configured to continuously sample the glucose level of the user and convert the sampled glucose level into a corresponding data signal for transmission by the transmitter 102. In one embodiment, the transmitter 102 is mounted on the sensor 101 so that both devices are positioned on the user’s body. The transmitter 102